1. Field of the Invention
The present invention relates to a method and apparatus for measuring molecular alignment and crystallinity of polymer fibers and films, and more particularly to a method and apparatus for measuring diameter, and birefringence of fibers in real time during production.
2. Related Art
In the field of synthetic fiber and film manufacturing, it is desirable to measure the molecular alignment, or crystallinity, of polymer fibers and films to determine the degree of solidification, or other characteristics of the fiber, at a particular time. When a fiber or film is created at a factory, it is drawn or stretched, which tends to orient the crystals. The fiber has an index of refraction across the length of the fiber and has another index of refraction along the length of the fiber. The difference between these indices of refraction is the birefringence of the fiber. The birefringence is a good indicator of the degree of crystallinity or degree of orientation of the crystals comprising the fiber. It is highly desirable to determine the birefringence of a fiber or a film during the production process while it is moving from a liquid state to a solid state. In the past, the only way to obtain such a measurement, has been to halt the manufacturing process, obtain a sample of the fiber or film and perform off-line analysis in a laboratory, where the fiber or film is immersed in calibrated oils until it disappears, which means the index of refraction of the surrounding material is equal to the index of refraction of the fiber. This is an expensive and time consuming process, and is very disruptive to the manufacturing process. Another problem is that a plurality of fibers are drawn from a spinner, which looks like a shower head, so it is impossible to position equipment in front and behind a particular fiber.
Accordingly, what is desired, and has not been heretofore developed, is a method and apparatus for measuring microstructures, anisotropy and birefringence in fibers and films during the production in real time, without interrupting the manufacturing process.
Previous attempts in this area include the following:
Massen, U.S. Pat. No. 4,887,155, which discloses a method of measuring or monitoring properties of yarns using an image sensor to obtain a two-dimensional image of a portion of the yarn which is converted to an electrical image signal. The signal is digitized and the values of the properties to be detected are determined. PA1 Siegel et al., U.S. Pat. No. 5,015,867, discloses a method and apparatus for measuring the diameter of a moving fiber using lasers and charged coupled devices for sensing the diffraction and interference patterns produced when electromagnetic radiation emitted from a laser is partially obscured by the edges of the strand. Information contained in the diffraction pattern may be extracted in a number of ways such as, for example, comparing the measured diffraction pattern with a theoretical pattern produced by a knife edge as calculated using the Kirchhoff-Fresnel integral. PA1 Noguchi, et al., U.S. Pat. No. 5,257,092, discloses a polarization and birefringence measuring device utilizing a wide polarized light beam to impinge on a specimen. A photo detecting sensor detects the light beam containing information about the specimen. An analyzer is used to vary the amount of light transmitted. A computer analyzes the polarization states of parts of the specimen corresponding to the samples taken. PA1 Rochester, U.S. Pat. No. 5,264,909, discloses a method and apparatus for measuring the diameter of an optical fiber as the fiber moves past the measuring apparatus. The device includes a number of discreet, stationery light sensors arranged in a linear array, a light source positioned to shine a beam of light onto the sensors of the array and a lens that directs an enlarged image of the optical fiber onto the array of light sensors. Each light sensor produces an output signal responsive to the intensity of light it receives. PA1 Urruti, U.S. Pat. No. 5,443,610, discloses an apparatus for controlling fiber diameter by taking two measurements of the fiber diameter and combining the measurements into a control signal. The first measurement is made on the bare fiber and the second measurement is made after a hermetic coating has been applied to the fiber. PA1 Ducharme, et al., U.S. Pat. No. 5,657,126, discloses an ellipsometer having a phase-modulated polarized light beam which is applied to a sample. Electric signals are obtained representing the orthogonal planes of polarization after the light has interacted with the sample and the constants of the sample are calculated from the two resulting electric signals. PA1 Yoshita, U.S. Pat. No. 5,619,325, discloses an ellipsometry optical system for analyzing light beams reflected from or transmitted through materials. The device includes a light source, a beam splitter, an optical frequency shifter for shifting a frequency of one of the light beams split by the beam splitter to form a reference light beam, a circular polarization converter for circularly polarizing the other light beam to form a probing light beam, a second beam splitter for combining the reference beam and the probing beam, a birefringence prism for receiving the combined beam and separating polarization components and a photo detector for converting the polarization components to electrical signals.
None of these previous efforts, taken either alone or in combination, teach or suggest all of the elements of the present invention, nor do they disclose all of the benefits and advantages of the present invention.